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#ifdef DEBUG
#define _GLIBCXX_DEBUG
#endif
//#pragma GCC optimize("O3")
#include<bits/stdc++.h>
using namespace std;

#ifdef DEBUG
#include "lib/debug.h"
#else
#define debug(...) 228
#endif

#define pb push_back

typedef long long ll;
typedef long double ld;
int n, c;
const int maxN = 500'005;
int a[maxN], w[maxN];
vector<pair<int,int>> f[maxN];
//for color
ll dp[maxN];
void umax(ll& a,const ll& b) {
    a = max(a, b);
}
int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    auto start = std::chrono::high_resolution_clock::now();
#ifdef DEBUG
    freopen("input.txt", "r", stdin);
#endif
    map<pair<int,int>,int> mp;
    cin >> n >> c;
    for (int i = 1; i <= n; i++) {
        cin >> a[i] >> w[i];
        mp[{a[i], w[i]}] += 1;
    }
    for (auto& it : mp) {
        f[it.first.first].emplace_back(it.first.second, it.second);
    }
    const ll INF = 1e18;
    for (int i = 1; i < maxN; i++) {
        dp[i] = -INF;
    }
    ll mx = c;
    for (int i = 1; i < maxN; i++) {
        if (f[i].empty()) continue;
//        debug(f[i]);
        vector<ll> upd(f[i].size(), -INF);
        ll S = 0;
        for (int j = 0; j < (int)f[i].size(); j++) {
            int cnt = f[i][j].second;
            //+a * cnt - c
            ll X = 1LL * cnt * i - c;
            S += max(0LL, X);
        }
        //X -> dp[t] + X - c}
        for (int j = 0; j < (int)f[i].size(); j++) {
            ll curS = S;
            int cnt = f[i][j].second;
            ll X = 1LL * i - c;
            curS -= max(0LL, X);
            umax(upd[j], mx + X);
            umax(upd[j], dp[f[i][j].first] + X + c);
        }
        /*for (int z = 0; z < 2; z++) {
            reverse(f[i].begin(), f[i].end());
            reverse(upd.begin(), upd.end());
            ll mxadd = -INF;
            for (int j = 0; j < (int)f[i].size(); j++) {
                ll curS = S;
                int cnt = f[i][j].second;
                ll X = 1LL * cnt * i - c;
                curS -= max(0LL, X);
                umax(upd[j], mxadd + X + curS);
                ll hisdelta = dp[f[i][j].first] + c + X - max(0LL, X);
                umax(mxadd, hisdelta);
            }
        }
        //1LL * cnt * i - c*/
        for (int j = 0; j < f[i].size(); j++) {
            umax(dp[f[i][j].first], upd[j]);
//            debug(dp[f[i][j].first]);
            umax(mx, upd[j]);
        }
    }
    cout << max(0LL, *max_element(dp + 1, dp + maxN)) << '\n';




    auto end = std::chrono::high_resolution_clock::now();
    std::cerr << "Execution Time: "
              << std::chrono::duration_cast<std::chrono::milliseconds>(end - start).count()
              << " ms" << std::endl;
    return 0;
}